The effects of acute total sleep deprivation (TSD) on brain function are not fully understood, particularly in the context of brain aging. There are significant parallels between the effects of TSD in young adults and the effects of normal aging on cerebral responses to cognitive challenges. For example, in both cases, neuroimaging studies have reported increased activation relative to well-rested young adults and some have interpreted these changes as compensatory in nature. This study will test the limits of the cerebral compensatory response to TSD by using functional magnetic resonance imaging (FMRI) to study healthy older adults, 60+ years-old, and young adults, 18-39 years-old, after normal sleep and after 36 hours TSD. Subjects will perform cognitive tasks assessing verbal learning and arithmetic working memory. This study will thereby test whether normal aging potentiates or inhibits the brain's compensatory response to TSD and whether this response differs with different cognitive demands. While no studies, to our knowledge, have used functional neuroimaging to examine the effects of TSD in older adults, behavioral studies suggest that older adults may be more resilient to TSD than younger adults. This raises the intriguing possibility that older adults will show even greater levels of activation after TSD than well-rested adults. Furthermore, this study will test whether this increased activation following TSD, if found, is associated positively with performance levels following TSD. This will help address whether these dynamic changes in cerebral responses to cognitive tasks after TSD are compensatory in nature or interfere with normal brain function. Specific Aims are: 1) to compare the cerebral response of adults aged 60+ years after normal sleep and after 36 hours TSD; 2) to determine if changes in cerebral responses after TSD are associated with changes in cognitive performance; and 3) to compare the neurocognitive effects of TSD in older adults and younger adults, aged 18-39. The overall goal of this program of research is to better understand and predict the neurocognitive effects of TSD. Additionally, this study will provide valuable information about the general plasticity and compensatory capabilities of the brain and may inform theories of brain aging.